1. Field of the Invention
This invention relates to an improved wave-damping underwater truss structure, and more particularly to an improved wave-damping underwater truss structure, in which an underwater truss includes a number of diagonal members arranged not parallel with each other and provided with one or more disc-shaped flanges (hereinafter referred to as a brim).
2. Description of the Prior Art
A wave-damping underwater truss structure is a light-weight offshore structure that substitutes for offshore structures such as a caisson breakwater and a tetrapod, whose wave-damping effects are attributable to their weight. This structure was invented by the present applicant so that it can inexpensively cope with weak ground. The principle structure of this wave-damping structure is disclosed in U.S. Pat. No. 3,864,049, and various types of improved structure of the wave-damping structure are disclosed in U.S. Pat. No. 4,074,497, Japanese Patent Publication 63(1988)-247413, Japanese Utility Model No. 1(1989)-180530 and Japanese Unexamined Patent Publication No. 2(1990)-70812.
Shafts and ball members are combined together to constitute a pyramid-shaped basic constitution such as an equilateral triangular pyramid, a square pyramid or the like. The shaft is provided with a brim or brims to increase a contact area per unit volume with which fluids come into contact, whereby the wave-damping capability of the truss structure is improved. This makes it possible to rationalize the entire size and economical efficiency of the structure to a much greater extent. The wave-damping underwater truss structure utilizes the feature wherein when waves pass through the underwater truss structure, the shape of the structure interferes with, and disturbs, the movement of the waves, so that the waves become turbulent and disappear as a result. This structure is characterized in that it serves as a wave-damping structure having a permeability for undulation.
In principle, this wave-damping structure can be expected to yield a considerable wave damping effect by changing undulation to turbulence and swirls. Because of its features, i.e., a relatively light weight, it is desired that this wave-damping underwater truss structure be put into practice. To this end, further advantageous improvements in the wave-damping structure are expected.
In the case of an existing wave-damping underwater truss structure that has been studied and developed up to the present, it is acknowledged that relatively small waves produced in a laboratory, that is, wave components having a high kinetic energy per unit spacing are damped to a significant extent. However, it came to light that such an existing wave-damping structure cannot sufficiently cope with sluggish waves such as "Tsunami", or tidal waves, and swell practically seen in the ocean. The existing wave-damping structure encounters the next problem of further improving the wave damping effect on these sluggish wave. It is considered especially difficult for a permeable wave-damping structure to dampen tsunami (tidal waves). Even a breakwater produced by the conventional gravimetoric method is also costly and technically limited. It is expected that a great depth breakwater having a truss constitution, which is eminently superior to a conventional one in reduced cost and construction period, will cope with the sluggish waves before the tsunami energy is excessively concentrated when the sluggish waves approach the seashore, so that the energy is wasted. In this point, however, this permeable wave-damping structure has an unchanging large permeability to the waves, thereby impairing the entire wave damping effect. For this reason, a drastic solution of such a problem is awaited.